Sorry for such a neophyte question, but I am wanting to know (aside from best practices - which I would never want to exceed nor challenge) if there is a default, maximum amount of Differential backups that can be run against a last good, known full? The reason I am asking is due to a migration that we are starting which is going to move one instance of databases to another server's instance, but the proof of concept that is wanted is to see if I was to take just one full - how many diffs can I run until another full is needed.

Thank you in advance, and again - just if there is an actual limit to how many diffs I can have before another full is needed is what I am needing to know.

There is no hard limit on the actual number of differentials you can have before a full backup is needed. With that said, however, it is good practice to periodically perform a full backup for performance and consistency reasons.